test(genesis/builder): canonical evmAddr/utxoAddr fixture parse gate (#121)

Add TestCanonicalGenesisFixtureParses — loads the canonical mainnet
genesis.json (genesis v1.12.19 evmAddr/utxoAddr field names) through
genesiscfg.GetConfigFile and asserts EVMAddr/UTXOAddr decode to
non-zero ids.ShortID values.

This is the "have we adopted the rename" gate — if the loader
silently swallows the new field names (e.g. via a regression to
ethAddr/luxAddr struct tags), every allocation Address comes back
as ShortEmpty and the assertion catches it before that ships.

Test is host-path aware: skips when ~/work/lux/genesis is not on
disk (CI without sibling checkout), runs when it is.

genesis/builder/canonical_fixture_test.go

@@ -0,0 +1,48 @@
+// Copyright (C) 2019-2026, Lux Industries Inc. All rights reserved.
+// See the file LICENSE for licensing terms.
+
+package builder
+
+import (
+	"os"
+	"path/filepath"
+	"testing"
+
+	"github.com/luxfi/ids"
+	"github.com/stretchr/testify/require"
+
+	genesiscfg "github.com/luxfi/genesis/pkg/genesis"
+)
+
+// TestCanonicalGenesisFixtureParses confirms the canonical mainnet genesis.json
+// (evmAddr/utxoAddr field names per genesis v1.12.19) parses cleanly via
+// GetConfigFile and produces non-zero EVMAddr / UTXOAddr values.
+//
+// This is the "have we adopted the rename" gate — if the loader rejects
+// the canonical fixture, the API rename did not land.
+func TestCanonicalGenesisFixtureParses(t *testing.T) {
+	candidates := []string{
+		filepath.Join(os.Getenv("HOME"), "work/lux/genesis/configs/mainnet/genesis.json"),
+		"../../../genesis/configs/mainnet/genesis.json",
+	}
+
+	var path string
+	for _, p := range candidates {
+		if _, err := os.Stat(p); err == nil {
+			path = p
+			break
+		}
+	}
+	if path == "" {
+		t.Skip("canonical mainnet genesis fixture not on disk; skipping")
+	}
+
+	cfg, err := genesiscfg.GetConfigFile(path)
+	require.NoError(t, err, "canonical fixture must parse with v1.12.19 evmAddr/utxoAddr names")
+	require.NotEmpty(t, cfg.Allocations, "fixture has no allocations")
+
+	for i, a := range cfg.Allocations {
+		require.NotEqual(t, ids.ShortEmpty, a.EVMAddr, "allocation[%d] EVMAddr is zero — parse silently dropped", i)
+		require.NotEqual(t, ids.ShortEmpty, a.UTXOAddr, "allocation[%d] UTXOAddr is zero — parse silently dropped", i)
+	}
+}